Mat of glass and other fibers in a separator of a storage battery

ABSTRACT

Methods and materials for producing microfibers, and methods or collecting the formed fibers as mats, either by themselves or with various additive, are disclosed. The mats are masses of intermeshed glass or other fibers produced by suspending the fibers in a gaseous medium, and collecting the suspended fibers on a foraminous material. The fibers suspended in the gaseous medium have a BET surface area of from 0.2 to 5 m 2  per gram. A method for adding additional materials to the mats is also disclosed; this method involves suspending the additives in the gaseous medium with the fibers.

REFERENCE TO RELATED APPLICATION

This is a continuation in part of application Ser. No. 08/923,876, filedSep. 2, 1997, now U.S. Pat. No. 6,071,641, granted Jun. 6, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of batteries and,more specifically, to batteries in which mat containing glass fibers,commonly called separators, are positioned between the positive andnegative plates and to a method for producing such mats or separatorsand batteries. As is subsequently discussed in more detail, separatorscontaining glass fibers are well known. Long before glass fiberseparators, however, cedar veneers were used as a separator material,and were replaced by microporous, hard rubbery separators and celluloseseparators impregnated with resins.

2. Description of the Prior Art

Valve regulated (“sealed”—“recombinant”) lead acid (VRLA) batteries areknown; they usually comprise a plurality of positive and negativeplates, as in a prismatic cell which can be a prismatic flat plate, orin layers of separator and positive and negative electrodes woundtogether, as in a “jelly roll” cell. The plates are arranged so thatthey alternate, negative - positive - negative, etc., with separatormaterial separating each plate from adjacent plates. The separator,typically composed of a mat of wet laid nonwoven glass fibers, is aninert material; it stores battery acid, and provides low electricresistance. In addition, in VRLA batteries, the separator materialprovides innumerable gas channels between the plates through whichoxygen can migrate from the positive electrode, when generated there, tothe negative electrode where it can be recombined with hydrogen,according to the oxygen cycle. Another important function of a separatoris to exert pressure against the plate paste or active material whichforces the paste into contact with the plate, and causes a pressurebetween the positive active material and the positive grid and betweenthe plates, ensuring that there is not an interface at which corrosion.which would cause premature capacity loss (PCL), can occur.

Glass fiber separator material has been produced commercially by wetprocesses on paper making equipment including fourdrinier machines androtoformers, inclined fourdrinier machines and extended wirerotoformers. In the production of separator made of glass fibers forVRLA batteries, it is preferred that no organic binder be added to afurnish from which separator sheets are made; the entanglement ofindividual microglass fibers serves to maintain the sheet in a cohesivestructure, and water glass or any of various sulfate salts, whichsometimes form on the fiber surfaces, serves as a binder. Organicbinders, however, tend to decrease the ability of a separator to wickacid, and to decrease the amount of acid a separator can hold. A greatdeal of work has been directed to modifying the glass fiber furnish fromwhich separators are produced to improve battery performance and/orlower the cost of the separator. Some of the work has entailed theaddition of synthetic fibers for various reasons, such as the use ofthermoformable plastic fibers so that the separator can be heat sealedon its edges to envelop a plate. Other work, which pertains to the fieldof this invention, has been directed to the use of a filler, e.g.,silica, or another siciciferous material, to provide separators whichare comparable to all glass fiber separators, at a lower cost.Separators made from glass fibers to which cellulose has been added andpolyolefin fibers to which cellulose has been added have also beensuggested. Prior art patents are discussed below.

U.S. Pat. No. 4,465,748 (Harris) discloses glass fiber sheet materialfor use as a separator in an electrochemical cell, and made from 5 to 35percent w/w of glass fibers less than 1 μm in diameter; the patent alsodiscloses a glass fiber sheet for such use wherein there are fibers of acontinuous range of fiber diameters and lengths, and most of the fibersare not over 5 mm in length.

U.S. Pat. No. 4,216,280, (Kono et al.), discloses glass fiber sheetmaterial for use as a plate separator in a battery, and made from 50 to95 percent w/w of glass fibers less than 1 μm in diameter and 50 to 5percent w/w of coarser glass fibers. The coarser glass fibers, thereference says, have a fiber diameter larger than 5 μm, preferablylarger than 10 μm , and it is advantageous for some of the coarserfibers to have diameters of 10 μm to 30 μm.

U.S. Pat. No. 4,205,122 (Minra et al.) discloses a battery separator ofreduced electric resistance comprising a self supporting, non woven matconsisting essentially of a mixture of olefinic resin fibers having acoarseness of from 4 to 13 decigrex and olefinic resin fibers having acoarseness of less than 4 decigrex, the latter fibers being present inan amount of not less than 3 parts by weight per 100 parts by weight offibers; up to about 600 parts by weight of inert filler materials per100 parts by weight of fibers can also be used. The battery separator isproduced by subjecting a suitable aqueous dispersion to a sheet-formingoperation, drying the resulting wet, non-woven mat, and heat treatingthe dried mat at a temperature ranging from a point 20° C. lower thanthe melting point of the aforementioned fibers to a point about 50° C.higher than the melting point.

U.S. Pat. No. 4,216,281 (O'Rell et al.) discloses a separator materialproduced from a furnish containing 30 to 70 percent w/w of polyolefinsynthetic pulp, 15 to 65 percent w/w of a siliceous filler and 1 to 35percent w/w of “long” fibers which can be polyester fibers, glassfibers, or a mixture of the two. Cellulose in an amount up to about 10percent w/w is disclosed as an optional ingredient of the furnish.

U.S. Pat. No. 4,336,314 (Yonnezu, et al), assigned to Japan StorageBattery Company, discloses a pasted lead acid battery with greatlyextended service life and capacity over the usuable service life therof.The battery has a glass mat, which may be of a dual layer construction,disposed adjacent positive plates of assembled elements. This patentteaches the importance of pressure that must be applied to the assembledelements, for example by a binding band, or from outside the batterycontainer. As the pressure applied to the elements increases, the patentsays, the charge and discharge cycle life increases although therelationship is said not to be linear. That is, in a pressure range offrom 40 to 60 g/dm², the life is abruptly increased by a factor of 2 to2.5 as the pressure increased. Therefore, up to about 100 kg/dm², thelife remains substantially unchanged. However, if pressure exceeds about100 kg/dm², the life decreases. The tendency to decrease depends on thetype of glass mat used. The life of the lead acid cell using the glassmat having a dual layer structure was found to be excellent at a lowpressure range while the life of such cell increases by a fator of abouttwo at a pressure of 20 kg/dm².

The patent also states that the pressure applied to the assembledelement presses on each plate and prevents the aforementioned expansioneffect attributed to changes in structure of the active material layer.During use, it is necessary to prevent a reduction of the degree ofpressure. It was found that the greatest cause for the reduction of thepressure applied to the assembled element is that, when the glass mat iswetted, its thickness decreases. The patent discloses that the degree ofreduction of pressure applied to the glass mat depends upon thetechnique used in fabricating the glass mat. In general it is statedthat it is desirable in a glass mat employed in a lead acid battery forthe degree of pressure applied when the mat is immersed in dilutesulfuric acid to be more than 70% of the degree of pressured applied inthe dry state. The importance of pressure was clearly noted and the mainsolution was external pressure devices. The method of making the glassmaterial was not stated but a Japanese disclosure, No. 5505306 JPA1issued to applicant: Japan Storage Battery Company Ltd., discloses adual layer glass mat produced by a wet laid process. U.S. Pat. No.4,336,314 refers to a Japanese Patent Office publication number,55091564 JP A1, which is said to have a date of publication of Jul. 11,1980.

U.S. Pat. No. 4,363,856 (Waterhouse) discloses a separator material madefrom a furnish composed of polyolefin pulp fibers and glass fibers, andnames polyester staple fibers, polyolefin staple fibers and cellulosepulp fibers as alternative constituents of the furnish.

U.S. Pat. No. 4,387,144 (McCallum) discloses a battery separator havinga low electrical resistance after extended use which is made by thermalconsolidation and thermal embossing of a paper web formed from a furnishcontaining a synthetic pulp composed of fibrils which are filled with aninorganic filler, the web incorporating a wetting agent which ispreferably an organic sulfonate, an organic succinate, or a phenolethoxylate.

U.S. Pat. No. 4,373,015 (Peters et al.) discloses sheet material for useas a separator in a battery, and “comprising organic polymeric fibers”;both of the examples of the reference describe the sheet material as“short staple fiber polyester matting about 0.3 mm thick”, and indicatethat the polyester fibers range from about 1 μm to about 6 μm indiameter.

Sheet separators for use in conventional (not valve regulated) batteriesand comprising both glass fibers and organic fibers are disclosed in allof the following U.S. Pat. No. 4,529,677 (Bodendorf); U.S. Pat. No.4,363,856 (Waterhouse); and U.S. Pat. No. 4,359,511 (Strzempko).

U.S. Pat. No. 4,367,271, Hasegawa, discloses storage battery separatorscomposed of acrylic fibrils in an amount of up to about 10 percent w/w,balance glass fibers.

Japanese patent document 55/146,872 discloses a separator materialcomprising glass fibers (50-85 percent w/w) and organic fibers (50-15percent w/w).

U.S. Pat. No. 4,245,013, Clegg et al., discloses a separator made byoverlaying a first sheet of fibrous material including polyethylenefibers with a second sheet of fibrous material including polyethyleneand having a synthetic pulp content higher than the first sheet.

U.S. Pat. No. 5,009,971, Johnson et al., discloses a porous flexiblesheet of about 93 to 99.5 weight percent amorphous precipitated silicaand from about 0.5 to about 7 weight percent fibrillated, unsinteredpolymeric material, e.g., polytetrafluoroethylene. The sheet is preparedby subjecting a dry homeogeneeous mixture of the silica and polymericmaterial, e.g., polytetrafluoroethylene, in the above proportions tomechanical shear blending forces to finrillate the polymer, andthereafter dry forming the resulting admixture into a sheet form.

U.S. Pat. No. 4,908,282, Badger, discloses a separator comprising asheet made from first fibers which impart to the sheet an absorbencygreater than 90% and second fibers which impart to the sheet anabsorbency less than 80% wherein the first and second fibers are presentin such proportions that the sheet has an absorbency of from 75 to 95%.This patent discloses that fine glass fibers have a high absorbency,that coarse glass fibers have a low absorbency, and that hydrophobicorganic fibers have an extremely low absorbency, and that, when thisseparator is saturated with electrolyte, unfilled voids remain so thatgas can transfer from plate to plate for recombination. The disclosureof Badger is incorporated herein by reference.

U.S. Pat. No. 5,091,275 (Brecht et al.) discloses a glass fiberseparator which expands when exposed to electrolyte. The separatorcomprises glass fibers which are impregnated with an aqueous solution ofcolloidal silica particles and a sulfate salt. The separator is producedby forming a paper making web of glass fibers, impregnating the web withthe aqueous mixture of silica and the salt, lightly compressing theimpregnated web to remove some of the aqueous solution, partially dryingthe web, compressing the web to a final thickness and completing thedrying of the web. The web is preferably compressed to a thickness whichis less than the distance between plates in a given cell, so thatinsertion of an assembled cell stack into a case is facilitated. Whenelectrolyte is added to the case, the salt dissolves in the electrolyteand the separator expands to provide good contact between the plates andthe separators. According to the patent, the silica contributes to therecombination performance of cells incorporating the precompressedseparator. The silica also contributes a great deal of stiffness to theseparator, so much so that the separator may be characterized as rigid.

It has been determined that the production of battery separator bypaper-making techniques from a furnish of glass fibers and silica powderleads to problems which are caused by variations in the concentration ofthe silica powder in the furnish. Typical glass fiber furnishes have aliquid content exceeding 98 percent w/w. In the course of makingseparator sheets, the furnish flows from a headbox onto an advancingscreen through which most of the water flows in the first few feet. Thewater, known as white water, is recycled and winds up back in theheadbox of the machine. If the furnish is composed exclusively of glassfibers, virtually none of the fibers pass through the wire and wind upin the white water. However, furnishes comprising glass fibers andsilica powder do not fare so well. In the absence of a retention aid,significant amounts of silica powder from such furnishes do pass throughthe paper making wire and wind up in the white water. Left unchecked,this phenomenon causes the concentration of silica powder in the furnishto increase, undesirably changing the properties of the furnish.Heretofore, the problem of silica powder and the like passing through apaper making wire has been avoided through the use of binders andretention aids.

U.S. Pat. No. 2,477,000 discloses a synthetic fiber paper produced fromfibrillae and fibers made by methods wherein a solution of the fiber isextruded through very small orifices (spinnerets).and the extrudedsolution is allowed to congeal in a precipitating bath, by evaporationof the solvent, or by temperature changes (see column 2, lines 25 andfollowing). The patent says that fibers of cellulose acetate, cellulosenitrate, regenerated cellulose from viscose, “Vinylite (a syntheticresin made by polymerization of vinyl compounds), Aralac (a fibrousproduct made from skim milk casein), and spun glass” which range inlength up to 1 inch and in diameter from 12-80 microns and fibrillaepreferably derived from flax, Manila hemp, caroa or hemp can be used tomake the paper. At least 90 percent of the fibrillae should be from0.0015 to 0.0025 inch in length and from 0.0000027 to 0.0000044 inch inwidth.

WO 98/12759, an International Application published Mar. 26, 1998,discloses “A resilient fibrous mat, preferably made of microfibers(which) is especially adapted for use as a battery separator for starvedelectrolyte batteries . . . The fibrous mat, with one or two surfacelayers, can be formed from an air laid fibrous blanket by subjecting oneor both surfaces of the blanket to hydro entanglement to increase theentanglement of the fibers at and adjacent the major surface(s) relativeto the entanglement of the fibers in the resilient fibrous layer. Thefibrous mat with a substantially uniform density may be made by floodingthe blanket with a liquid and drawing a vacuum through the blanket.”

European Patent Application 97116846, Japan Vilene Co., Ltd., filed Sep.29, 1997, published as EP 0834932 A2, shows the kind of entanglementdisclosed in WO98/12759 to produce the material of FIGS. 1 and 2thereof, but applied to the entire body of the separator material ratherthan to a region or regions adjacent one or both major surfaces as inWO98/12759.

An English language abstract of a published Japanese patent application(07147154, published Jun. 6, 1995), entitled SEPARATOR FOR ALKALINEBATTERY states:

“A fiber having a section form shown in (c) of the drawing, for example,is constituted from 0.04 to 0.12 deniers of circular and petalpolypropylene component 2 and 0.12 denier of a polyethylene component 1.A hundred percent of this dividing composite fiber with a fineness of 2deniers and a fiber length of 38 mm is opened by a card machine tolaminate unidirectional and cross fiber webs with METSUKE of 1.3 and 52f/m². This is treated from both surfaces with a water flow having awater pressure of 130 kg/cm² on a nozzle plate having a nozzle diameterof 0.13 mm and a pitch of 0.6 mm. This cloth is dipped in fumingsulfuric acid, sulfonated, and then calendered to provide a separatorhaving a METSUKE of 65 g/m² and a thickness of 0.15 mm. The sametreatment can be performed in constitutions other than (c) in thedrawing. Thus, excellent electrolyte resistance, oxidizing property, andliquid holding property are provided, and a battery can be smoothlyoperated for a long period.”

BRIEF DESCRIPTION OF THE INSTANT INVENTION

The instant invention is based upon the discovery that a binderlessglass fiber mat suitable for use as a separator for Valve regulated(“sealed”—“recombinant”) lead acid (VRLA) batteries can be produced by adry process by collecting the fibers from fiberizing apparatus, withoutsubjecting them to a wet paper making or other post forming process, andselecting portions of the collected fibers which are sufficientlyuniform in thickness and grammage for use as battery separators. In apreferred embodiment, fibers can be entwined by the air flow in acollection duct to produce a superior separator material. In contrast,the use of the wet process to produce separators typically necessitatesbaling of the glass fibers as produced, and their redispersion to form aweb. The requirement of making glass microfibers for use as apapermaking fiber requires that, unless the fibers are degradedexcessively in the papermaking process, the fiber is manufactured to asuitable shorter length than would otherwise be possible to enable thefiber to undergo subsequent operations in the papermaking process. Theprocess of delivering a fiber to a wet process paper machine (sometimescalled a “former”) usually requires the baling of the fibers, openingthe bales, adding the open bales into a mixer commonly referred to as apulper, and then expending sufficient energy to disperse or break apartthe fibers in the water slurry so that adequate uniformity of the fibersin the slurry is achieved. A description of the art can be found in apaper published by TAPPI Press in the 1985 Nonwoven Symposiumproceedings (ISSN 0272-7269). The paper is entitled “Important FactorsIn Glass Web Manufacturing” (Frey, et al ). Some important issues whichare discussed in the paper emphasize the value of the instant discovery.The paper states, concerning stock preparation, that the dispersion ofglass microfibers is a critical step in the manufacture of glass papers.The fibers are very brittle and are easily reduced to sand if too muchenergy is used for dispersion. Table 1 of the paper lists pulping, pH,water temperature, stock consistency and pulping time as importantvariables having been named by either manufacturer's literature orpapers published by the manufacturers.

Rotary fibers have been described as more easily dispersed than flame/attenuated fibers and also as being more easily damaged by excessagitation. Flame attenuated fibers can also be seriously damaged by toomuch pulping. In general the minimum amount of agitation required toachieve acceptably uniform distribution of the glass fibers is used.

It is also known to one skilled in the art that even the packaging offibers can cause difficulty in dispersing them. In short, thepapermaking process requires the fibers to have been manufactured sothat they can be suitably dispersed; any shortcomings in the fiberforming process must be offset by an increase in the amount of energyemployed in producing a slurry to achieve a suitable uniformity of thefiber in the final separator. Increased degradation of the fibers is aconsequence of any increase in the amount of energy employed inproducing the slurry.

The relationship between the fiber forming process and the energyrequired to produce a satisfactory paper-making slurry from the fibersproduced is noted in Manville Tempstran® Battery Separator Applicationdata sheet MFI printed 12/86. This data sheet discusses the TempstranMicro-fiber as producing superior separator paper, which means anarticle of manufacture made by the wet laid process. The ManvilleTempstan publication quotes the following:

“Fiber dispersion is accomplished in typical pulping equipment such as aHollander beater or HCV hydropulper. Pulping should be of minimumduration, only long enough to open up and separate the fibers. Utilizeminimum shear to maintain maximum fiber length since fiber entanglementis a prime bonding mechanism.”

It should be noted that Manville is known today as Johns Manville and isthe largest producer of mcirofiber for the wet laid process Even acurrent patent application, WO 98/12759, filed by Johns Manville,although it discusses the problems with papermaking, as noted above,fails to show an appreciation that it is possible to select separatormaterial to achieve the requisite degree of uniformity or that it ispossible to control the glass fiber making process so that longer fiberscan be produced, and can be entwined by the air flow in the collectionduct

As is noted above, one of the principle attributes of microglassseparator is that it imparts to the VRLA battery in which it is used thecompression resiliency of the microglass. Nevertheless, as can be seenfrom the above discussion the prior art had produced a sheet that hadfiber length that had to be made shorter and less entangled to allow forsubsequent dispersion. This produced a sheet that was less than optimumfor the separator to impart the most force onto the paste andsubsequently to the paste-grid interface. Therefore, another aspect ofthe instant invention is an improved separator made by a dry process,and composed of fibers having greater lengths that would be possible inwet laid separator. The fibers in this separator can be speciallytwisted and entangled to provide for improved compression-recoveryproperties by readjustment of airflow collection ducting, temperature ofthe glass melt, the glass chemistry to affect such properties of theglass as the liquidus temperature and the manner of collecting andforming of the microglass fibers. Also, since the fibers do not need tobe redispersed, additives can be introduced during the collectionprocess to enhance the properties of the separator.

Glass fibers produced by the flame blown process, which is subsequentlydescribed in more detail, can be conveyed to, and wound on a drum untila mat weighing about 1,000 grams per square meter has been collected;the mat can then be slit transversely, and removed from the drum assheets weighing about 1,000 grams per square meter. having one dimensionwhich equals the circumference of the drum, and another which equals thewidth of the drum. This mat, which has, in a typical example, an averagefiber diameter of 0.8 μm, can be separated into layers having the weightin grams per square meter desired in a given battery separator, and thelayers can be cut to size and used as separators, as subsequentlydescribed in more detail. Web having the targeted grammage can also betaken directly from the drum or from the conveyor before it reaches thedrum. In the alternative, glass can be fiberized by another method whichis controlled so that a continuous sheet having the targeted grammage isproduced.

A glass fiber mat which can be used in practicing the instant inventioncan also be made by what is called “the rotary process” in glass formingapparatus which includes a glass melting tank, a rapidly rotatingcentrifugal bushing with small openings in a periphery, at least onehigh pressure hot gas nozzle from which a high velocity fiberizing jetis directed across the periphery of the centrifuge, and a collectingconveyor. Molten glass fed to the centrifugal bushing is caused bycentrifugal force to flow through the peripheral openings of the bushinginto the fiberizing jet, by which the streams of glass are attenuatedand carried onto a collecting conveyor which is pervious to the gas. Themat from this process can also be collected on a drum, slittransversely, and removed from the drum as sheets which, again can weighabout 1,000 grams per square meter, and can be composed of fine fibers,average fiber diameter 0.8 μm when the rotary process is that of U.S.Pat. No. 5,076,826, or can range up to about 3 μm when other rotaryprocesses are used. This mat can also be separated into layers havingthe weight in grams per square meter desired in a given batteryseparator, and the layers can be cut to size and used as separators, assubsequently described in more detail. This web having the targetedgrammage and thickness can also be taken directly from the drum, or fromthe conveyor before it reaches the drum.

It has been found by examination, using a scanning electron microscope,of mat produced as described in the two preceding paragraphs andcollected on a drum, that the mat is formed in discrete layers, each ofwhich is composed of the fibers deposited during one revolution of thecollecting drum, and that there is a fiber diameter gradient within eachof the discrete layers, the fibers of the smallest diameter beingconcentrated adjacent one major surface of each layer, and the fibers ofthe largest diameter being concentrated adjacent the other majorsurface. A part of the increased resilience of battery separatoraccording to the invention is attributed to the observed layering, andanother part is attributed to the gradient in fiber diameter within eachlayer. It will be appreciated that separator material can also beproduced by a wet papermaking process where similar layering occurs, forexample, by casting a plurality of slurries of glass or other fibers,the first on the screen of paper making apparatus, and the second andsubsequent ones on the previously cast fibers, or by assembling aplurality of thin sheets of glass or other fibers made by a wet processto produce a composite separator having the desired thickness andgrammage. Accordingly, in one aspect, the invention is a batteryseparator composed of a plurality of thin sheets of non-woven fabricassembled to constitute the separator, and the thin sheets can be madeby an air-laid or by a wet process.

Thinner sheets of the glass fiber mat can also be produced by either theflame blown process or by the rotary process, including that of U.S.Pat. No. 5,076,826, and enough of the thinner sheets to provide thedesired grammage, which usually ranges from about 20 to about 1000 g.m⁻²can be stacked, and then cut to size. To produce the thinner sheets,glass fibers can be produced from softened glass and collected in aconventional manner, usually on a foraminous conveyor, and the speeds ofthe fiberizing process and of the conveyor can be set so that a mathaving the desired grammage is conveyed from the forming operation, andeither rolled for future use, or cut to size, in which case it can beused immediately to produce batteries, or stacked for future use. Thecontinuous sheet can also be collected with a cross-lapper to improveits uniformity. The continuous or sheeted material can also be enhancedby additional processes such as precompressing the material to provideimproved ease of battery assembly or improved thickness control. Variousadditives can also be introduced into the mat to improve otherproperties as required by the specific separator.

When a battery is produced, at least one stack of alternating positiveand negative plates is assembled, with separator between adjacentplates, and the separator of each stack is compressed so that the stackcan be slipped into a pocket which is a part of the case of the battery.It is important that the separator have sufficient resiliency, aftersuch compression, that it exerts the required pressure against the pasteor active material on each plate to force the paste into contact withthe plate, and to cause a pressure between the plates, ensuring thatthere is an interface, along the faces of the plates, among the platepaste or active material, the electrolyte and oxygen. A standard testhas been developed to measure the resiliency of a separator material.The results of this test, as is subsequently explained in more detail,indicate that separators in batteries according to the invention aresignificantly more resilient than otherwise identical separators madefrom different samples of the same glass fibers, but by a conventionalwet paper making process.

OBJECTS OF THE INVENTION

It is, therefore, an object of the instant invention to provide animproved VRLA or other battery containing a separator composed, at leastpredominantly, of glass fibers as collected from a fiber formingprocess, i.e., without having been subjected to a wet paper makingprocess or to a post forming process such as that called an “airlaid” orspunlaced, or to another post forming, secondary process

It is another object to provide a method for producing a batteryseparator composed predominantly of glass fibers.

It is yet another object to provide a glass fiber VRLA separator whichhas better resiliency than a separator made by the wet paper makingprocess from the same fibers.

It is yet another object to provide a glass fiber VRLA separator whichhas better resiliency than a separator made by the wet paper makingprocess from the same fibers and by which the fibers retain their fiberlength to a greater percentage.

It is yet another object to provide a glass fiber VRLA separator that iscomposed of longer fibers of the same fiber diameter than would bepresent in such a separator made from the same fibers by a wet papermaking process.

It is still another object to provide a glass fiber VRLA batteryseparator which has greater resiliency, by comparison with previouslyknown separators, and, as a consequence, can be 10 to 50 percent lighterin weight per unit of area (grammage) but still provide the same “BCI”(Battery Council International) thickness as conventional wet laidseparator, i.e., 300 grams per square meter for separator having a BCIthickness of 2.13 millimeters, which is determined by measuring thethickness of a one square inch portion of the separator when a load of1.5 psi is applied to a one square inch footer which bears on thatportion of the separator.

It is yet another object to provide a VRLA battery separator which hasimproved resilience and shock absorbing properties because it iscomposed of a plurality of separate layers.

It is a further object to provide a glass fiber VRLA separator which hasgreater absorbency for a battery electrolyte than does a separator madeby the wet paper making process from the same fibers.

It is still another object to provide a glass fiber VRLA separatormaterial in which the average fiber length is greater than in aseparator made by the wet paper making process from the same fibersbecause the fiber breakage associated with the paper making or postforming redispersing and forming processes does not occur.

It is yet another object to provide a separator that is composed ofmultiple, separately formed layers of glass or other fibers.

It is yet another object to provide a separator that is composed ofmultiple, separately formed layers of glass or other fibers and hassiliciferous materials added into the separator to enhance the drip rateof the separator and increase the surface area to influence theabsorption and deabsorption of the electroylte during the charge anddischarge reactions of the battery.

It is yet another object to provide a separator that is composed ofmultiple, separately formed layers of glass or other fibers or otherpolymers to improve toughness, wetability, or both of the separator.

It is yet another object to provide a separator that is composed ofmultiple, separately formed layers of glass or other fibers withinorganic salts and binders added, and that has been pressed to form apress compressed separator that has greater compression resiliency thana comparable wet laid separator.

It is yet another object to provide a separator that is composed ofmultiple, separately formed layers of glass or other fibers withinorganic salts and binders added, and that has been pressed to form apress compressed separator that, has greater compression resiliency thana comparable wet laid separator and placed in a battery so that asemi-jelled battery can be produced by the addition of sulfuric acidwithout the need for adding silica to the acid introduced into thebattery.

It is still a further object to provide a Separator which has a givenmean BET thickness, produced by suspending fibers in air or another gas,and collecting the suspended fibers on a foraminous conveyor.

It is still a further object to provide a process and a material made bythe process wherein, after the fibers are formed and while they arebeing attenuated, other additives that have been introduced into the airmixture that is supplied by the center air supply tube ale introducedinto the mat to provide enhanced physical properties of the compositematerial so formed. The material so produced has utility as a separator,but can also have utility as a filter medium, thermal insulation orsound barrier medium. The additives that can be introduced includesiliceriferous materials, inorganic salts, organic particles, andthermal binders to mention a few.

It is still a further object, in a method for producing a glass fibermat which includes introducing air to the fiberizing process through acentral supply air duct, to introduce into the central duct a modifierwhich coats the fibers as they are formed and makes them adhesive sothat they can be adhered to a porous or solid web, film or foil.

Other objects and advantages will be apparent from the description whichfollows, reference being made to the attached drawings.

DEFINITIONS

As used herein, the term “percent v/v” means percent by volume; the term“percent w/w”and the symbol % mean percent by weight; the term “wire”,as applied to a paper making machine, means the surface of the machineon which a furnish is cast in producing paper, and can be, for example,the screen of a Fourdrinier machine or the vacuum drum of a rotoformermachine; pore sizes reported herein, unless otherwise indicated, are inmicrons, and are determined by the first bubble method or by liquidporosimetry, Coulter; all temperatures are in ° C.; all grammages arereported herein in grams per square meter, but ill determinations aremade in grams per square inch of separator material and are converted tograms per square meter; and the following abbreviations have themeanings indicated: μm=micron or microns; mg=milligram or milligrams;g=gram or grams; kg=kilogram or kilograms; l=liter or liters;ml=milliliter or milliliters; cc=cubic centimeter or cubic centimeters;pcf=pound per cubic foot or pounds per cubic foot; m=meter or meters;cm=centimeter or centimeters; mm=millimeter or millimeters;mil=inch×10⁻³ or inches×10⁻³ (multiply times 25.4 to convert to mm);kPa=pressure in thousands of Newtons per square meter: psi=pounds persquare inch (multiply times 6.89 to convert to kPa); and kN=force inthousands of Newtons.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view with parts broken away to show details ofconstruction of a VRLA battery according to the invention.

FIGS. 2 and 2a are vertical sectional views which show different partsof apparatus for producing a glass fiber mat by what is called “therotary process”; the mat can be used as collected from the fiber formingprocess, i.e., without having been subjected to a wet paper makingprocess, to produce a battery according to the invention; together,FIGS. 2 and 2a constitute a schematic representation of the apparatus.

FIG. 2b is a view in vertical section which shows a different embodimentof the apparatus of FIG. 2a; in the embodiment of FIG. 2b, glass fibermat produced by the rotary process is used directly as separatormaterial in producing assemblies comprising positive and negative platesand separators for use in batteries.

FIG. 2c is a vertical sectional view which shows still anotherembodiment of the apparatus of FIG. 2a; in the FIG. 2c embodiment, glassfiber mat produced by the rotary process is rolled for future use asseparator material in producing batteries.

FIG. 3 is a schematic representation similar to a part of the apparatusof FIG. 2a, showing different apparatus which can be used to produce aglass fiber mat by what is called “the flame blown” process; theapparatus of FIG. 3 can be used alone to produce a mat or with theapparatus of FIG. 2 to produce a glass fiber mat that can be used ascollected from the fiber forming process to produce a battery accordingto the invention.

FIG. 4 is a schematic representation similar to FIG. 3 of still anotherapparatus which can be used with that of FIG. 2 for producing a glassfiber mat that can be used as collected from the fiber forming processto produce a battery according to the invention.

FIGS. 5 and 7 are plots of thickness in mm of separator materials thatcan be used in batteries according to the invention, when compressed(the compression curve), vs. force in kPa applied to compress theseparator to that thickness and of rebound thickness in mm (the reboundcurve) vs. force applied before rebound thickness was determined.

FIGS. 6 and 8 are plots of the data represented in FIGS. 5 and 7 and, inaddition, plots of thickness of a wet-laid glass fiber separator in mmwhen compressed vs. force in kPa applied to compress the separator tothat thickness and of rebound thickness in mm vs. force applied beforerebound thickness was determined for commercial separator materials thathave been used in batteries.

FIG. 9 is a plot of separator thickness in mm against compression forcein kPa for each of two different materials under compression, andrebound thickness for each of the same two materials after they haverecovered after being unloaded.

FIG. 10 is a vertical sectional view which shows, schematically,apparatus similar to that of FIG. 3 for producing a glass fiber mat bywhat is called “the flame blown method”; the mat produced can be used ascollected from the fiber forming process, i.e., without having beensubjected to a wet paper making process, to produce a battery accordingto the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A single cell battery according to the invention with a total of 9plates is indicated generally at 10 in FIG. 1. Except for the identityof the separator material therein, the battery 10 is conventional; theseparator can be used in other otherwise conventional batteries. Thebattery 10 comprises four positive plates 11 which are electricallyconnected to a positive terminal 12 and five negative plates 13electrically connected to a negative terminal 14. The plates 11 and 13are housed within a battery case 15 which is covered by a top 16. Thereis an opening through a boss 17 on the top 16 of the battery. Separators18 are composed of sheets of separator material wrapped around thebottom and both major faces of each positive plate 11.

In a specific example, five, 8A-U1 batteries similar to the batteries10, but having four negative and four positive plates were produced fromseparator material composed of glass fibers collected, as the fiberswere formed, into a mat weighing about 310 g.m⁻²; the fibers had anaverage diameter of substantially 0.8 μm. A control battery was alsoproduced using a separator that is commercially available under thedesignation BG 30005: this material, which is made by the wet papermaking process, weighs 300+/−15 g.m⁻². This control was made so thatassembly and properties of the five 8A-U1 batteries could be comparedwith the assembly and properties of a control made with separator havingthe same general target grammage. It was noted that the drylaidseparator used to produce the five batteries had a substantially greaterthickness and resiliency that the control separator: this confirmedlaboratory findings concerning drylaid separator. An assembly of threepairs of positive and negative plates with the drylaid separator hadapproximately the same thickness as an assembly of five pairs ofpositive and negative plates with the BG 30005 separator, indicatingthat drylaid separator for a given battery should have aboutthree-fifths the grammage of conventional wetlaid separator for thatbattery.

Difficulties were encountered in the assembly of the batteries from thedrylaid separator because of the high resiliency of the airlaidseparator. These difficulties arose when attempts were made to caststraps on the assemblies of plates with separators and in insertingassemblies of plates and separators into batteries. The cases ofbatteries that were made were deformed by forces exerted by theseparator. One assembly of plates and drylaid separator was compressedin a press with one ton of force for fifteen minutes; since the platesurfaces were 4.85 inches by 4.85 inches, this amounted to an appliedforce of about 87 psi. This assembly was then inserted into a batterycase, which it did not deform.

In another example, batteries similar to the batteries 10, but having 4positive plates and 4 negative plates were assembled using sheets cutfrom the rest of the separator, which had a grammage of about 250g.cm⁻². Separators were placed between adjacent plates, but were notused between the case and the outer plates. The batteries were found tohave cycling characteristics substantially equivalent to those of thecontrol battery. In another specific example, a glass fiber mat wasproduced which weighed 1000 g.m⁻² and was composed of fibers having anaverage diameter of substantially 0.8 μm; a layer which weighed 318g.m⁻², which was separated from this mat, is the separator in thebattery described above in this paragraph. The separator was subjectedto testing to determine “Compression” and “rebound”. Compressionthicknesses were determined by the method described in U.S. Pat. No.5,336,275 under various applied loads, and after the excess of eachapplied load above 3.79 kPa was released; the former measurements are he“Compression” thicknesses while the later are “rebound” thicknesses. Theaverage results are presented graphically in FIG. 5, which is a plot ofthe thicknesses of the separator 18 in mm (designated A) at variousapplied loads in kPa and of the thicknesses in mm (designated B) afterthe excess above 3.79 kPa of each applied load was released. Each datapoint for one of the curves of FIG. 5 is indicated by “+” (this is thecurve for “rebound” thickness) and each data point for the other curveis indicated by a dot (this is the curve for “Compression” thicknesses).The data plotted in FIG. 5 indicate that the separator is an outstandingmaterial. Compression and rebound thicknesses were determined for acommercially available separator material that is produced by a wetprocess using paper making equipment. The material tested is availableunder the trade designation HOVOSORB BG 30005, grammage 318 g.m⁻². Theaverage results of this testing are presented graphically in FIG. 6,which is a plot similar to FIG. 5, showing the data plotted in FIG. 5and the Compression thicknesses (designated C) of the HOVOSORB BG30005separator in mm and the Rebound thicknesses in mm (designated D) againstthe applied load in kPa.

In yet another specific example, a glass fiber mat weighing 1000 g.m⁻²was produced. The mat was composed of fibers having an average diameterof substantially 0.8 μm; a layer which weighed 130 g.m⁻² was separatedfrom this mat and used as the separator in the battery 10. The separatorwas subjected to “Compression” and “rebound” testing. The averageresults are presented graphically in FIG. 7, which is a plot of theCompression thicknesses of the separator in mm (designated E) and of therebound thicknesses in mm (designated F) against the applied load inkPa. The data points for one of the curves of FIG. 7 are shown by plusmarks (these are the data points for the “Rebound” curve), while thosefor the other curve are indicated by dots (these are for the“compression” curve). The data plotted in FIG. 7 indicate that theseparator is an outstanding material. Compression and reboundthicknesses were determined for a another separator material that iscommercially available, this one under the trade designation BGC 14065,grammage 130 g.m⁻². The average results of the BGC 14065 material arealso presented graphically in FIG. 9, which includes a plot of thecompression thicknesses of the BGC 14065 separator in mm (designated G)and of the rebound thicknesses in mm (designated H) against the appliedload in kPa. The data points for one of the BGC 14065 curves are shownby open circles (these are the data points for the “Rebound” curve),while an * indicates each data point for the other BGC14065 (these arethe “compression” curves).

In still another specific example, glass fiber mat weighing 1000 g.m⁻²was used to produce separator material. The mat was composed of severallayers of intermeshed fibers, one of which was collected on eachrotation of a collecting drum. The fibers of the mat had an averagediameter of substantially 0.8 μm; each layer weighed substantially 130g.m⁻². Rectangles of the size desired for separators were selected byvisual examination from the layers of the mat for minimum variations inthickness and grammage, and were cut from the mat for use as batteryseparator.

Compression and rebound testing of other separator materials composed ofthe 608 MF mat which ranged in grammage from 130 to 1151 g.m⁻²,indicated that they are all outstanding separator materials.

In another example, a glass fiber mat was produced which weighed 258g.m⁻² and was composed of fibers having an average diameter ofsubstantially 0.8 μm. This separator was subjected to “Compression” and“rebound” testing. The average results are presented graphically in FIG.9, which is a plot of the Compression thicknesses of the separator in mmand of the rebound thicknesses in mm against the applied load in kPa.The data points for one of the curves of FIG. 9 (designated I) are thedata points for the “Rebound” curve), while those for another curve(designated J are for the “compression” curve). Compression and reboundthicknesses were also determined for a wetlaid separator material,grammage 244 g.m⁻². The average results of the wetlaid separatormaterial are also presented graphically in FIG. 9, showing thecompression thicknesses of the wetlaid separator in mm (designated K)and the rebound thicknesses in mm (designated L) against the appliedload in kPa.

It has been considered desirable for glass fiber separator material usedin VRLA batteries to contain a substantial proportion of fine fibers,e.g., finer than about 5 μm. The separators, if +hey contain asufficient proportion of fine fibers, are capable of holding enough ofthe relatively small amount of electrolyte that is used in suchbatteries to make contact with the plates, and to enable an electriccurrent to flow through the separators. It is usually desirable that theseparators also contain a substantial proportion of coarser fibers inorder to reduce the cost per pound. The cost performance of a separatoris as critical as improvement in the physical properties of theseparator for this technology. The ability to manufacture a separator atreduced cost is the main focus of all separator manufacture and is a keypart of most work done on separator material. The coarse fiber, inaddition to helping to reduced the cost of the separator, also provideschanges in separator physical properties that may improve theperformance of the VRLA battery, depending on the design use of thebattery. Increasing the fiber diameter (decreasing the surface area ofthe fiber blend) can increase the rate at which the battery manufacturercan fill the battery with electrolyte because the rate of wicking forthe typical plate heights in most VRLA batteries will increase, asreported in a paper given by George C. Zguris at the Fifth InternationalILZRO Lead Acid Battery Seminar. This seminar was held Apr. 18, 1991 inVienna, Virgina. Additional information can also be found in anotherpaper authored by Zguris, Klauber and Lifshutz entitled “NewDevelopments in Control of Valve-Regulated Battery Separators”, whichhas also been presented. This higher rate of wicking is the effect of ahigher distribution of larger pores caured by the larger fibers. Therate of wicking determines how quickly the sulfuric acid electrolytefills, or drips into the battery. The larger pore structure alsoprovides for easier fluid flow and release of the sulfuric acidelectrolyte into or from the plates. The blending and layering of thefiber can be seen to be advantageous to a battery manufacturer becauseit makes possible greater efficiency in the filling of the batteries.The filling process for VRLA type batteries is much more complex thanfor what is described as a conventional flooded lead acid battery. Oneof the disadvantages faced by the manufacturer is that the VRLA batteryis higher in cost compared to the flooded lead acid battery. Some ofthis disadvantage to the VRLA battery manufacturer is that it takes muchlonger to fill the VRLA battery than to fill conventional floodedbatteries; also additional equipment such as vacuum fillers must beemployed to get the acid into the separator and the plates. A separatorthat enables improvements in the filling process presents an advantageto the manufacturer of VRLA batteries. In addition to the time requiredto fill the battery it is important that when the battery is filled ithas the correct amount of electrolyte for a conventional 100% glassseparator material to allow for sufficient recombination to occur. Aseparator that is 100% saturated and does not follow the disclosures ofU.S. Pat. No. 4,908,282, Badger, will not allow for recombination tooccur because the oxygen that is generated at the positive plate can notmove to the negative plate. Most VRLA batteries will therefore be madewith only 90-95% of the separator pore spaces filled with theelectrolyte. As the amount of electrolyte is decreased, therecombination reaction increases. Therefore, providing a separator thathas higher porosity between the plates will provide an enhancement tothe battery, since additional acid can be added with the same level ofrecombination. Since the amount of sulfuric acid in the battery relatesto the capacity of the battery, such a separator provides for a batterywith improved low rate capacity. The coarse fiber is also a disadvantagein the battery because, as the fiber surface area is decreased, thecycle performance of the battery also decreases. This was disclosed inU.S. Pat. No. 4,336,314, Yonnezu. The impact of the fine fiber to coarsefiber ratio and how this impacts cycle life has also been disclosed inpress releases and papers presented and released by the Advance LeadAcid Battery Consortium (ALABC). Therefore, to enhance a separator it isimportant that one consider the combined impact of having a suitableblend or blends of fiber diameters to provide a battery having asuitable fill rate and a suitable cycle performance. With conventionalwet laid microglass separators these two important properties areopposite in nature; if a change improves the filling rate, the cycleperformance of the battery is adversely affected. It is the goal of anyseparator improvement to increase the acid fill rate and yet provide forequal or improved cycle life.

Drylaid mat produced as described above has been examined under ascanning electron microscope. It was observed that the material whichwas collected on a drum while that drum rotated more than one revolutionwas composed of a plurality of discrete layers, one for each rotation ofthe drum during the collection process, and that there was a fiberdiameter gradient within each of the discrete layers, the fibers of thesmallest diameter being concentrated adjacent one major surface of eachlayer, and the fibers of the largest diameter being concentratedadjacent the other major surface. The tests described above demonstratethat this separator material has improved resilience, by comparison withwetlaid separator. An experiment that has been performed with pluralsheets of wetlaid glass fiber separator demonstrated that the separatorcomposed of discrete layers also has improved shock resistance bycomparison with conventional wetlaid separator. The experiment involutedcompressing a stack of wetlaid separator sheets using a compressionfixture on a conventional tensile testing machine. Scanning electronmicroscope examination of the compressed material revealed thatsubstantially all of the deformation occurred in one of the outsidesheets of the stack. This indicates that the layered separator materialwould also have improved shock resistance by comparison with materialwhich is substantially uniform throughout its thickness. It will beappreciated that the separator material can also be produced by a wetpapermaking process where similar layering occurs, for example, bycasting a plurality of slurries of glass or other fibers, the first onthe screen of paper making apparatus, and the second and subsequent oneson the previously cast fibers, or by assembling a plurality of thinsheets of glass or other fibers made by a conventional wet process toproduce a composite separator having the desired thickness and grammage,

It will also be appreciated that dry-laid webs of fibers made by theprocess described in Chapter 7: Dry-Laid Systems by Albin F. Turbak,“Nonwovens. Theory, Process, Performance, and Testing” can also be usedas separator material in batteries according to the present invention.This process involves carding bundled fibers that can be purchased frommanufacturers, and suspending the carded fibers in air or another gasinside a hood, and using vacuum to draw the suspended fibers onto aforaminous conveyor so that they form a web of a desired thickness.

FIGS. 2 and 2a show apparatus which can he used to produce batteryseparator material composed of first glass fibers having a first averagefiber diameter and second glass fibers having a second average fiberdiameter. The apparatus has two different fiberizers, one of which isindicated generally at 19, and the other of which if indicated generallyat 19′. The two fiberizers 19 and 19′ are identical, each includes aspinner assembly 20, 20′ carried by a rotatable spindle 21, 21′ whichcan be rotated at high speed about its longitudinal axis 22, 22′ by amotor (not illustrated) which drives a belt-driven pulley 23, 23′ thatis keyed to the tipper end of the spindle 21,21′.

Each of the spinner assemblies 20. 20′ includes an internal bowl 24, 24′which rotates with the spindle 21, 21′. Each bowl 24, 24′ has aperipheral wall 25, 25′ through which there are several small diameteropenings 26, 26′. Each spinner assembly 20, 20′; also has an insulatingheat shield 27, 27′ which minimizes heat loss from the bowl 24, 24′.

As each spinner assembly 20 20′ is rotated, molten glass 28, 28′ flowsfrom a melting tank (not illustrated) through a tube 29, 29′ into one ofthe bowls 24, 24′ from which centrifugal force causes streams of theglass to flow through the openings 26, 26′. An annular nozzle 30, 30′surrounds each of the spinner assemblies 20, 20′. Combustion of a fuelgas in a chamber 31, 31′ forces a jet of heated gas to flow downwardlythrough the nozzles 30, 30′.

The gas jets flowing from the nozzles 30, 30′ attenuate streams ofmolten glass which flow through the openings 26, 26′ into fine fibers32, 32′ and direct them downwardly onto a conveyor 33, 33′ where theycollect as a mat.

Each fiberizer 19 and 19′ also includes a riser tube 34, 34′ which isconnected to a source for compressed air (not illustrated) and to an endtube 35, 35′ which extends vertically upwardly, and terminates justbelow the heat shields 27, 27′. As is indicated by arrows 36, 36′, airflows upwardly through the riser tubes 34, 34′ and the end tubes 35, 35′until it is deflected outwardly by the spinner assembly against theinterior of a veil 37. 37′ of fibers inside housings 39 and 39′.

The fiberizers 19 and 19′ are disclosed in U.S. Pat. No. 5,076,826,which explains that the upward flow of air indicated by the arrows 36,36′ prevents a low pressure zone beneath the spinner assemblies 20, 20′,and, as a consequence, reduces the amount of remelt which forms in thefiber veils 37, 37′. The patent also discloses that the fiberizers,except for the parts thereof which cause the upward flow of air, wereprior art. Glass fiber mats produced by this apparatus that have beenmarketed are not sufficiently uniform in thickness and in grammage foruse of separator material.

The apparatus of FIGS. 2 and 2a can be operated to produce separatormaterial for use in batteries according to the invention. For example,the fiberizers 19 and 19′ can both be operated to produce fibers havingan average diameter of 0.8 μm, in which case the speed of the conveyors33 and 33′ can be controlled so that a mat 38 having the desiredgrammage is accumulated on the conveyors before it is conveyed fromwithin the housings 39 and 39′ for delivery to an upwardly inclinedconveyor 40 and collection on a take-up roll 41. Ultimately, the mat 38can be slit to width and used, for example, as described in U.S. Pat.No. 5,344,466 to produce batteries.

Alternatively, the fiberizer 19 can be operated to produce fibers havingan average diameter of 0.8 μm, and the fiberizer 19′ can be operated toproduce fibers having a larger fiber diameter, say 1.5 μm, and the speedof the conveyors 33 and 33′ can be controlled to provide mat having adesired grammage and a desired proportion of fibers of the twodiameters. Since it is usually desirable that the finest fibers of aseparator be adjacent the plates of a battery, two layers of theseparator described in this paragraph can be placed on top of oneanother, with their coarse fiber sides adjacent one another, to providea particularly advantageous separator material.

Another apparatus (not illustrated) that can also be used to produceseparator material composed of two outer layers of fine fibers and acenter layer of coarser fibers comprises the apparatus of FIGS. 2 and 2aplus a third fiberizer, identical to the fiberizers 19 and 19′ which ispositioned between the two so that it deposits fibers on a mat that hasalready been formed in the fiberizer 19 and the fiberizer 19′ depositsfibers on the mat discharged by the third fiberizer. In this case, thefiberizers 19 and 19′ are preferably operated to produce fine fibers,and the third fiberizer is operated to produce coarser fibers.

The length of microfibers produced in the apparatus of FIGS. 2 and 2adepends upon glass chemistry. Slight changes can be made to impactvarious properties of the glass. Since the glass is ultimately exposedto sulfuric acid the chemistry must be controlled to provide a low acidsolubility. The acid solubility can be determined in various ways. Inaddition to the acid solubility the elements that are leached from theglass is also critical. As an example the amounts of iron, platimum,nickel and zinc leached from the separator is important Some examples ofhow chemistry influences the glass fiber process are as follows: theaddition of zircon to E-glass raised its liquidus temperature; which isthe highest temperature at which a glass, if held there sufficientlylong, will develop crystals, thus increasing the risk that the glasswill devitrify, either before or after forming. It will be appreciatedthat the presence of even submicroscopic crystals in a glass melt isdisastrous for fiber manufacture, because such a crystal can interruptthe flow of glass which is necessary in producing fibers. In general, itis desirable for a glass to be fiberized to have a low liquidustemperature, and for the liquidius temperature to be substantially belowthe fibrising temperature so that the glass is stable during fiberizing(see, for example, The Manufacturing Technology of Continuous GlassFibres, K.L. Loewenstein, 1993 Elsevier Sciene Publsihers). Small levelsof fluoride assist in the melting of a glass, lowering the liquidustemperature and making fiber formation easier. In some cases, traceelements added to improve glass properties either in the melt or duringfiber forming, must be balanced with the performance inside the battery.For example, a low level of iron is desirable in a glass fiber inside abattery, but the presence of iron oxide in the glass has a significantinfluence on the stability of the fiber forming operation because ironincreases the rate of infra-red emission. This influences the rate thatheat is radiated from the glass fiber as it leaves the fiber formingoperation. Increasing the sodium content of the glass, lowers theliquidius temperature, and increases the acid solubility, but does nothave a negative influences in the battery; in fact positive resultswould be expected, because, for a VRLA battery, sodium sulfate isusually a desirable additive in the electrolyte.

Referring to FIG. 3, still another apparatus that can be used inproducing separator material that can be used in a battery according tothe invention is indicated generally at 42. The apparatus 42 comprises afiber collection zone 43 in which primary filaments 44 drawn by pullrolls 45 from a fiber forming bushing 46 in a glass melting tank 47 passover a filament support 48 and into a blast of hot gases from a highpressure hot gas nozzle 49. The blast of hot gas softens the filaments,attenuates them into fine fibers 50, and projects them to the rightinside the collection zone 43. As is indicated by arrows 51, atmosphericair can enter the region where the fibers 50 are projected. A glassfiber mat 52, which can be one discharged from the fiberizer 19 entersthe collection zone 43 on a conveyor 53, which passes over a suction box54, holding the mat 52 in contact with the conveyor 53, and drawingfibers 50 to the bottom of the collecting zone 43 and onto the mat 52and a mat 55 which forms inside the collection zone as fibers 50 aredeposited, first, onto the mat 52, and then onto fibers 50 that havepreviously been so deposited.

The mat 55 can be conveyed into the fiberizer 19′ for augmentation, orit can be slit, stacked, and used as previously described to produce abattery according to the invention, or it can be wound on a roll forsubsequent processing.

Referring to FIG. 4, still another apparatus that can be used inproducing separator material that can be used in a battery according tothe invention is indicated generally at 56. The apparatus 56 comprises afiber collection zone 57 in which a strand 58 of textile glass fibers isdrawn by pull rolls 59 to pull individual fibers 60 from a textile fiberbushing (not illustrated) in a glass melting tank (not illustrated),through a gathering shoe 61 and to second pull rolls 62 by which it isdirected into a blast of gases from a high pressure gas nozzle 63. Theblast of gas breaks up the strand 58, and projects the fibers 60 to theright inside the collection zone 57. A glass fiber mat 64, which can beone discharged from the fiberizer 19, enters the collection zone 57 on aconveyor 65, which passes over a suction box 66, holding the mat 64 incontact with the conveyor 65, and drawing fibers 60 to the bottom of thecollecting zone 57 and onto the mat 64 and a mat 67 which forms insidethe collection zone as fibers 60 are deposited, first, onto the mat 64,and then onto fibers 60 that have previously been so deposited.

The mat 67 can be conveyed into the fiberizer 19′ for augmentation, orit can be slit, stacked, and used as previously described to produce abattery according to the invention, or it can be wound on a roll forsubsequent processing.

The apparatus of FIGS. 2 and 2a can also be used to produce a multilayerseparator material, e.g., by operating the fiberizing apparatus 19 ofFIG. 2 to deposit a mat composed of a thin layer of fine fibers on theconveyor 33, advancing this thin layer of mat into the fiberizingapparatus of FIG. 2a, and depositing additional fibers and asiliciferous material, e.g., silica, sand, clay, talc, fumed silica,precipitated silica, sericite, colloidal silicia, silicate of soda,silicate, silicon alkoxide, vermiculite, volcanic ash, wollastonite,zircon, forsterite, diamtomaceous earth, cutlet, cristobalite, glassflakes, or aluminium silicate on top of the thin layer of mat. Thefibers can be deposited in the apparatus of FIG. 2a as previouslydescribed, and an aqueous slurry of the silica or the like can be fed ata suitable rate to a rotating dish 67 With veins 68 so that the slurryis thrown outwardly by centrifugal force in the dish 67 and thenprojected radially outwardly by the veins 68 into the veil 37. Any ofthe slurry that falls onto the thin layer of the mat on the conveyor 33′is merely collected there, becoming a part of the separator materialjust like that which impinges on the veil 37. The procedure justdescribed can also be used to deposit both silica and a sulfate salt inthe apparatus of FIG. 2a. In that case, the FIG. 2 apparatus can beoperated to deposit a mat composed of a thin layer of fine fibers on theconveyor 33, advancing this thin layer of mat into the fiberizingapparatus of FIG. 2a, and depositing additional fibers and an aqueoussolution of colloid silica particles or of colloidal silica particlesand a sulfate salt onto the single layer or multilayer separator. Thefibers can be deposited in the apparatus of FIG. 2a as previouslydescribed, and an aqueous slurry of the silica or of the silica and asulfate salt can be fed at a suitable rate to the rotating dish 67 withveins 68 so that the slurry is thrown outwardly by centrifugal force inthe dish 67 and then projected radially outwardly by the veins 68 intothe veil 37. Any of the slurry that falls onto the thin layer of the maton the conveyor 33′ is merely collected there, becoming a part of theseparator material just like that which impinges on the veil 37. A sprayunit, curtain coater, size press unit or other suitable delivery device,can also apply the solution. The mat discharged from the fiberizer 19′is then compressed and the excess fluid is removed by a suitable dryingdevice. while the separator is held in its compressed condition, so thatthe dried separator is pre-compressed in the sense that the separator,when in a battery, will expand upon the addition of sulfuric acid to thebattery. The separator just described is an improvement over that ofU.S. Pat. No. 5,091,275, (Brecht et al.) in that the process ofpapermaking is eliminated so that the fibers therein are longer. withthe result that the separator has improved compressibility.

Sulfate salts and colloidal silica introduced into the separator asdescribed in the preceding paragraph can cause the separator to becomevery stiff and rigid. Separators which contain amounts of colloidalsilica and sulfate salts sufficient to cause this rigid condition aredifficult to dry with conventional dryers usually used to dry wetprocess separator. It is also part of the present invention that thesalts can bred kept towards the middle of the sheet so that theseparator has less rigid outer layers, with the result that initialcontact between separator and battery, plate is improved. It is also tobe understood that organic binders that would release the fibers withinthe cell once the sulfuric acid electrolyte is added can be used. Thesoluble binder can be a starch, a gum, sodium carboxymethyl cellulose,Hydroxyethyl cellulose, or any of various wet strength additives. Sincethe separator of the instant invention has much more resiliency, and fora given grammage would have a greater thickness, a pre-compressedmaterial could be used as a separator to provide the samegrammage-thickness relationship as a separator made by a wet laidprocess, so that an increased wet compresive force can be maintainedinside the battery. It is well known that the force with which a typicallass separator resists compression is less when the separator issaturated with electrolyte to levels found inside a lead acid batterythan when the separator is dry. The change in this force call be a 20-60percent decrease from that when the separator is dry. A process thatdecreases this difference will enhance the battery. In many cases, thedry compressive force that must be applied for a separator to havesufficient resilience after the acid is added exceeds the force that canbe withstood by the battery case; this makes it impossible for amanufacturer to assemble the battery without defects. Such defects couldbe poor sealing between the case and the cover, intercell partitionleaks, or poor cast on strap welds, to name a few. Thus, a separatorwith a decreased dry-wet force ratio or a separator that provides agreater thickness in the wet condition offers a substanstial advantage.

The apparatus of FIGS. 2 and 2a can also be used to produce a singlelayer or multilayer separator material composed of polyolefin fibers,usually polyethylene or polypropylene. For example, streams 28, 28′ of amolten polyolefin can flow from a melting tank (not illustrated) throughthe tubes 29, 29′ into one of the bowls 24, 24′ from which centrifugalforce causes streams of the polyolefin to flow through the openings 26,26′ so that heated gas jets flowing through the nozzles 30, 30′attenuate the polyolefin streams into fine fibers 32, 32′ and directthem downwardly onto the conveyors 33, 33′. Air flowing upwardly throughthe riser tubes 34, 34′ and the end tubes 35, 35′ is deflected outwardlyby the spinner assembly against the interior of a veil 37, 37′ ofpolyolefin fibers inside the housings 39, 39′.

The fiberizing apparatus 19 of FIG. 2 can be operated to deposit a matcomposed of a thin layer of fine polyolefin fibers on the conveyor 33,and this thin layer of mat can be advanced into the fiberizing apparatusof FIG. 2a where additional polyolefin fibers can be deposited onto thesingle layer or multiple layer separator. If desired, an aqueoussolution of colloidal silica particles or of colloidal silica particlesand sulfate salt can also be introduced in the apparatus of FIG. 2a. Thepolyolefin fibers can be deposited in the apparatus of FIG. 2a aspreviously described. The mat discharged from the fiberizer 19′ is thencompressed and the excess fluid, if any, is removed by a suitable dryingdevice, while holding the thickness of the separator in its compressedcondition, so that the dried separator is pre-compressed in the sensethat the separator, when in a battery, will expand upon the addition ofsulfuric acid to the battery.

Fiberizing apparatus other than that of FIGS. 2 and 2a can also be usedto produce separator according to the invention, so long as care istaken to collect the fibers produced so that the separator issufficiently uniform in thickness and in grammage. For example, theapparatus of FIGS. 3, 4 and 10 can be so used, as can the modificationsof FIGS. 2b and 2 c, and other “flame blown” and other “rotary”processes, e.g., those which do not include the tubes 39 and 39′ ofFIGS. 2 and 2a. It will be appreciated, however, that fiberizingapparatus which includes the tubes 39, 39′ is highly desirable becauseof the ease with which additives such as silica can be mixed uniformlywith the fibers.

Similarly, the apparatus of FIGS. 2 and 2a can be used to produce stillanother multilayer separator material, e.g., by operating the fiberizingapparatus 19 of FIG. 2 to deposit a mat composed of fine fibers on theconveyor 33, advancing this layer of mat into the fiberizing apparatusof FIG. 2a and depositing additional fibers and a siliciferous materialof extremely fine particle size, which can be added as a concentratedsiliciferous slurry or as a dry powder. Such siliciferous powders ofspecially prepared silicon dioxide are also known as fumed silicia orSiO₂ and are especially beneficial. Colloidal silica, which iscommercially available from duPont, could also be used. The presence offinely divided silica in the separator enables improved retention of theacid. When the silica content is sufficiently high that the separatorcauses the acid to gel, this result is achieved without the difficultstep of adding the fumed silica to the sulfuric acid electrolyte in thebattery. This gel usually forms when the separator contains at least5-6% of the fumed silica, based upon the weight of the electroylteultimately added to the battery.

The addition of fumed silica to a battery to which the electrolyte hasalready been charged requires the acid to be chilled, high energyintensive agitation, or both to prevent premature gelling of theelectrolyte before the addition of the silica is complete. The instantinvention provides a dry, glass-silica separator; the silica in theseparator causes the gelling of the electrolyte, so that the silica doesnot have to be added into the sulfuric acid, with the result thatcharging of the electrolyte is easier, and the possibility that theelectrolyte will jell prematurely is eliminated. Separators containing agelled electrolyte are usually composed of microporous polyethlyene orPVC. The fumed silica in such a separator should usually constitute from30-50% of the total weight of the separator. It has been found byscanning electron microscope examination that the silica is far frombeing uniformly distributed in separators containing silica that haveheretofore been known. The silica is much more uniformly distributed inseparators according to the invention which contain silica.

It will be appreciated that, for some applications, a separatorcontaining a given percentage of a fine silica adjacent one of the majorsurfaces will be desirable while a different percentage of a fine silicawill be desirable adjacent the opposed major surface. For example,silica can be introduced in the apparatus of FIG. 2a to control porestructure of the separator to provide a match to the pore structure ofone of the facing plates of a battery in which the separator is to beused, while the apparatus of FIG. 2 is operated to produce materialwhich contains no silica. Similarly, separator can be produced bydepositing only fibers from the apparatus of FIG. 2, depositing fibersand a given proportion of silica from a first unit of the apparatus ofFIG. 2a, and then depositing fibers and a different proportion of silicafrom a second unit of the apparatus of FIG. 2a.

The apparatus of FIGS. 2 and 2a can also be used to produce stillanother multilayer separator material, e.g., by operating the fiberizingapparatus 19 of FIG. 2 to deposit a mat composed of fine fibers on theconveyor 33, advancing this layer of mat into the fiberizing apparatusof FIG. 2a and depositing additional fibers and a concentrated slurry ofextremely fine cellulose or other fibrils, e.g., acrylic, on top of thelayer of mat. The fibers can be deposited in the apparatus of FIG. 2a aspreviously described, and an aqueous slurry of the cellulose fibrils canbe fed at a suitable rate to the rotating dish 67 so that the slurry isthrown outwardly by centrifugal force in the dish 67 and then projectedradially outwardly by the veins 68 into the veil 37. Any of the slurrythat falls onto the thin layer of the mat on the conveyor 33′ is merelycollected there, becoming a part of the separator material just likethat which impinges on the veil 37. There can also be a dish 67 (notillustrated) in the fiberizer 19 of FIG. 2, which can be operated asjust described to introduce cellulose fibrils into the fibers formed inthe fiberizer 19.

Referring now to FIG. 10, apparatus indicated generally at 69 is similarto that of FIG. 3, except that a drum collector 70 has been substitutedfor the conveyor 53 of the FIG. 3 apparatus. The apparatus 69 comprisesa fiber collection zone 71 in which primary filaments 44 drawn by pullrolls 45 from a fiber forming bushing 46 in a glass melting tank 47 passover a filament support 48 and into a blast of hot gases from a highpressure hot gas nozzle 49. The blast of hot gas softens the filaments,attenuates them into fine fibers 50, and projects them to the rightinside the collection zone 71. As is indicated by arrows 51, atmosphericair can enter the region where the fibers 50 are projected. A mat 72which is collected on a foraminous surface 73 of the drum 70 is removedfrom the drum by a roll 74 from which it is delivered to a collectionzone, not shown.

A modification of the apparatus of FIG. 2a is shown in FIG. 2b,designated 19″. Most of the components of the apparatus 19′ of FIG. 2aare present in the apparatus 19″ of FIG. 2b, and are designated by thesame reference numerals. In the FIG. 2b apparatus, glass fiber mat 38that has been collected on the conveyors 33 (FIG. 2) and 33′ (FIG. 2b)is delivered to a conveyor 75, passes between compression rolls 76, overa roll 77, and is delivered to apparatus indicated generally at 78. Theapparatus 78 trims the mat 38 to a desired width and produces a cellassembly from the trimmed separator and other components. The cellassembly is described in U.S. Pat. No. 5,344,466, and shown in FIG. 3thereof, while the portion of the apparatus 78 which produces the cellassembly is described in the patent, and shown in FIG. 5 thereof. A flatpressing operation can be substituted for that performed by thecompression rolls 76 in the apparatus of FIG. 2b, or the mat can becompressed by passing between parallel open belts. These pressingoperation can also be carried out in an oven.

A modification of the apparatus of FIG. 2a is also shown in FIG. 2c,designated 19′″. Most of the components of the apparatus 19′ of FIG. 2aare present in the apparatus 19′″ of FIG. 2c, and are designated by thesame reference numerals. In the FIG. 2c apparatus, glass fiber mat 38that has been collected on the conveyors 33 (FIG. 2) and 33′ (FIG. 2c)is delivered to a conveyor 79, passes between compression rolls 80, andis collected on a roll 81. The rolls of separator material can beshipped or transported to a remo-te or nearby battery assemblyoperation. The mat can also be cut to size by suitable apparatus andstacked for shipment or transportation to a remote or nearby batteryassembly operation

It will be appreciated that the instant invention, as described above,may be subjected to various modifications without departing from thespirit of the invention disclosed and claimed herein. For example,separator according to the invention and comprised of a plurality ofsheets or layers may be needled or sewn together to provide addedphysical integrity for the separator. Additionally or alternatively,layers of material can be cross-lapped. In addition, additives which donot affect the essential characteristics of the separator may beincorporated, and can be added, in the apparatus of FIGS. 2a, 2 b and 2c by charging them to the dish 67, or can be introduced into the risertubes 34, 34′. Other modifications and changes will be apparent to oneskilled in the art, and can be made without departing from the spiritand scope of the invention as defined in the appended claims.

I claim:
 1. In a storage battery comprising a plurality of lead platesin a closed case, a fibrous sheet plate separator between adjacent onesof said plates, and a body of a sulfuric acid electrolyte absorbed byeach of said separators and maintained in contact with each of theadjacent ones of said plates, the improvement wherein said separatorsheets consist essentially of intermeshed glass or organic fibersproduced by suspending fibers in a gaseous or liquid medium, andcollecting the suspended fibers on a foraminous material in at leastfour discrete layers, with the proviso that the mass of fibers has a BETsurface area of from 0.2 to 5 m² pergram.
 2. In a storage battery asclaimed in claim 1, the improvement wherein the collected fibers arepredominantly glass microfibers.
 3. In a storage battery as claimed inclaim 1, the improvement wherein the collected fibers are predominantlyorganic microfibers.
 4. In a storage battery as claimed in claim 1, theimprovement wherein an inorganic particulate material is suspended andcollected with the fibers, and the inorganic particulate materialconstitutes from 5 to 90 percent of the total weight of the fibers andparticulate material.
 5. In a storage battery as claimed in claim 1, theimprovement wherein the fibers are suspended in a liquid medium.
 6. In astorage battery as claimed in claim 1, the improvement wherein thefibers are suspended in a gaseous medium.
 7. In a storage battery asclaimed in claim 1, the improvement wherein the suspended and collectedfibers are predominantly glass microfibers and chopped glass strandfibers.
 8. In a storage battery as claimed in claim 1, the improvementwherein the suspended and collected fibers are glass microfibers,chopped glass strand fibers or both and from 5 to 95 percent w/w organicfibers.
 9. In a storage battery as claimed in claim 8, the improvementwherein the organic fibers are polyolefin fibers.
 10. In a storagebattery as claimed in claim 8, the improvement wherein the organicfibers are Sulfar fibers.
 11. In a storage battery as claimed in claim8, the improvement wherein the organic fibers are polyester fibers. 12.In a storage battery as claimed in claim 8, the improvement wherein theorganic fibers are acrylic fibers.
 13. In a storage battery as claimedin claim 8, the improvement wherein the organic fibers are cellulosefibers.
 14. In a storage battery as claimed in claim 8, the improvementwherein at least some of the organic fibers are bi-component fibers. 15.In a storage battery as claimed in claim 14, the improvement wherein thebi-component fibers act as a binder for the separator to improve thetoughness of the separator, the cycling characteristics of the battery,and the resistance of the battery to vibration.
 16. In a storage batteryas claimed in claim 15, the improvement wherein said operator, when inthe wetted condition, has a mullen bursting strength which is higherthan that of an otherwise identical, 100% microglass separator when inthe dry, as received, condition.
 17. In a storage battery as claimed inclaim 15, the improvement wherein the maximum mullen bursting strengthof the separator is at least twice that of an otherwise identical, 100%microglass separator.
 18. In a storage battery as claimed in claim 8,the improvement wherein the suspended glass fibers are a mixture ofmicrofibers and chopped glass strand fibers.
 19. In a storage battery asclaimed in claim 4, the improvement wherein the inorganic particulatematerial increases the BET surface area of the separator by at least 100m²/g and improves the stratification of the battery during float orcycle applications.
 20. In a storage battery as claimed in claim 1, theimprovement wherein the compositions of the several layers differ fromone another.
 21. In a storage battery as claimed in claim 1, theimprovement wherein the fibers in the separator have a mean length whichis only 10% shorter than the mean length of fibers in a mat suitable foruse to produce a separator by the wet laid process.
 22. An improvedstorage battery as claimed in claim 21 which is a lead acid battery. 23.An improved storage battery as claimed in claim 22 which is a VRLAbattery.
 24. An improved storage battery as claimed in claim 23 in whichthe separator consists essentially of glass fibers.
 25. In a storagebattery as claimed 1, the improvement of a fibrous sheet plate separatorwhich consists essentially of intermeshed glass fibers produced bysuspending glass fibers in a gaseous medium, collecting the suspendedglass fibers on a foraminous material, and separating the collectedfibers from the foraminous material, with the proviso that the fiberssuspended and collected have a BET surface are of from 0.2 to 5 m² pergram, and with the further provisos that the separator has a mean fiberlength equal to the original fiber length of a fiber made and collectedfor a wet laid process.
 26. An improved storage battery as claimed inclaim 25 which is a lead acid battery.
 27. An improved storage batteryas claimed in claim 26 which is a VRLA battery.
 28. In a storage batteryas claimed 1, the improvement of a fibrous sheet plate separator whichconsists essentially of intermeshed glass fibers produced by suspendingglass fibers in a gaseous medium, collecting the suspended glass fiberson a foraminous material, and separating the collected fibers from theforaminous material, with the proviso that the fibers suspended andcollected have a BET surface area of from 0.2 to 5 m² per gram, and thefurther proviso that the mean length of the fibers in the separator isgreater than the mean length of fibers manufactured for use to produce aseparator by a wet laid process.
 29. An improved storage battery asclaimed in claim 25 which is a lead acid battery.
 30. An improvedstorage battery as claimed in claim 26 which is a VRLA battery.